Hunt for gravity points to parallel universes

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A dramatic proposal, reported in Scientific American, looks at how gravity can be included in an explanation of the fundamental forces of nature. The new theory predicts the existence of parallel universes and could be proven with in 10 years.

Nima Arkani-Hamed of the United States Department of Energy's Lawrence Berkeley National Laboratory, Savas Dimopoulos of Stanford University, and Gia Dvali of New York University propose that there may be other dimensions, apart from the three familiar dimensions of space and one of time that we all know.

The theory can be tested in particle accelerators, and proof, expected within 10 years, would cause the biggest upheaval in fundamental physics since Isaac Newton saw the apple fall in 1665.

It's a worldview that opens bizarre landscapes - including possible parallel universes coexisting with our own, in real space and near enough to touch. The familiar world may inhabit a kind of "membrane" in a multidimensional "bulk" of possible universes.

Scientists have long assumed that G, the gravitational constant Newton devised to calculate the attractive force between masses at different distances, is fundamental and unchanging. However, Arkani-Hamed and his colleagues suggest we have little reason for assuming that G is fundamental. "It has only been measured down to about a millimeter," he said. "What if gravity is actually as strong as the other forces at distances we haven't measured yet?"

These new dimensions are perhaps as large as a millimeter or may be too small to see. This, they suggest, is why the standard model of particle physics has not been able to give a common explanation for gravity.

Although we think of gravity as strong - we can get hurt if we fall down - compared to electromagnetism, gravity is astonishingly weak. It takes the gravity of the whole Earth to hold a pin on a tabletop: a toy magnet can lift it easily. Why then is it so weak? The researchers say, perhaps gravity only seems weak. If electromagnetism and the forces that act on quarks are confined to the familiar three dimensions of space and one of time, while gravity is free to propagate in all dimensions, only part of its effects would be experienced.